Problem: If $5a + 6b = 6$ and $7x + 8y + 5z = -2$, what is $45a - 49x + 54b - 56y - 35z$ ?
Solution: $= 45a + 54b - 49x - 56y - 35z$ $= (9) \cdot (5a + 6b) + (-7) \cdot (7x + 8y + 5z)$ $= (9) \cdot (6) + (-7) \cdot (-2)$ $= 54 + 14$ $= 68$